Conventional real-time fluoroscopic X-ray imaging involves directing an X-ray beam through an object to impinge onto a scintillator that converts the X-rays into energy in the visible spectrum. The scintillator is typically a layer of luminescent or phosphorescent material that is capable of generating visible light in response to being stimulated by the X-ray beam. When the X-ray beam passes through portions of the object under examination that are opaque to varying degrees to X-ray wavelengths, e.g. bone or metal, a shadow defining the configuration and position of the opaque portion is formed. The resultant visible light shadow is then typically intensified and reduced in size prior to being transmitted by video means, observed by a technician, and/or recorded. Intensification is conventionally achieved by use of a cesium iodide scintilator demagnifying intensifier tube. Conventional fluoroscopic X-ray imaging systems are used commonly for medical, security and industrial applications.
Systems have been developed for converting the X-ray shadow image to a digital signal to conveniently display or record the image or to transmit the image via television. These digital systems commonly utilize a flat panel detector, essentially a planar array of photosensors or CCDs (charge coupled devices) connected to electronic apparatus. One such system is disclosed in U.S. Pat. No. 6,895,077 entitled SYSTEM AND METHOD FOR X-RAY FLUOROSCOPIC IMAGING. The visible light beam created in the scintillator projects to a portion of the array to activate a photosensor receptor that is connected to an output cable. The sum of all the photosensor receptors equates to a total screen picture. To create a moving image, as is common in fluoroscopic imaging for observing internal organs or guiding arthroscopic surgery, the array of photosensors receives a changing image over time and transmits sequential panels of information. As a result, the digital flat panel is analogous to 20th century motion picture technology in which an individual frame was exposed, then the film advanced to expose a subsequent frame. By exposing many frames in succession, a live-appearing sequence, or motion picture, was created. Standard motion picture speed captures and displays at a rate of at least 16 frames per second to achieve a realistic motion sequence. In the flat panel X-ray system, a maximum image capture rate of 10 frames per second can be achieved. This capture rate, based on photosensor-digital technology, is insufficient to approach real-time motion viewing that is needed to accurately explore an object or guide an operative procedure. Thus the use of digital imaging is not effective and it is essential to transmit the image in analog format to achieve real-time quality. Digital flat panel imaging devices are neither real-time (i.e. fluoroscopic) nor high resolution (less than 7 lp/mm).
As with all imaging formats, image sharpness is a major concern. In the case of visible spectrum converted X-ray imaging, whether medical, security, or industrial, image resolution can be crucial. Image resolution is defined in units of line pairs (a line and a space) per millimeter (lp/mm), that is, the maximum number of line pairs that can be observed in a millimeter of width and distinguished as separate lines. In other words, resolution determines the smallest distinguishable white space between two parallel lines. Prior fluoroscopic X-ray image systems have achieved resolution of up to 5 lp/mm. For acceptable clarity, a resolution of at least 12 lp/mm is needed to visualize small details and comprehend their importance. For example, an X-ray examination of an implanted vascular stent must be sufficiently clear to identify minute problems that occasionally occur. Simply magnifying a small image that is of low resolution will merely provide an unclear larger image. Reducing the size of a large image to intensify the pattern also fails to achieve detail clarity. Early fluoroscopic systems included a scintillator that projected visible light energy to a demagnifying image intensifier which transmitted a smaller image to a camera device. These systems use unacceptably high X-ray dosage, and deliver relatively poor image resolution, on the order of 5 lp/mm or less.
Image resolution could, theoretically, be enhanced by increasing the intensity or dose of the X-ray beam. However, an increased dose X-ray beam has serious physiological implications both for the patient being examined fluoroscopically and for the medical technician. Thus it is important to reduce X-ray dosage as much as possible. The U.S. Food And Drug Administration monitors radiation relating to the use of fluoroscopic guidance of minimally invasive internal procedures, e.g. angioplasty. The FDA guidelines list time exposures of X-rays that have been shown to cause skin damage resulting from a dose of 2.0 Rads/minute. Longer time at a given radiation dose can cause greater damage, both to the skin and to internal organs. Lower dose rates are deemed to be safer.
Therefore, a need exists for a high resolution fluoroscopic X-ray system capable of magnified real-time motion perception and generated from use of a low dose X-ray beam. The invention disclosed below provides such an X-ray fluoroscope.